A conventional component mounting head will be described with reference to the drawings.
FIG. 8 shows a perspective view of the whole of a mounting apparatus. Nozzle members 2 for holding with suction electronic components to be mounted to circuit boards are attached at a front end part of a component mounting head 1. Each nozzle member 2 can be attached/detached to the component mounting head 1 in a one-touch operation. A nozzle station 3 provides nozzle members 2 in conformity with components to be mounted.
As mentioned above, while the nozzle members 2 can be freely attached/detached to the component mounting head 1, for this free attachment/detachment, three types (1)--(3) of component mounting head 1 have been proposed.
The structure of a mounting head and a nozzle member in a prior example (1) will be first described with reference to FIGS. 4 and 5.
In FIG. 4, a fitting part 4a of a nozzle member 4 is formed cylindrical and having an air path 11 thereinside. The fitting part 4a is detachably fitted at a front end part in a vacuum rod 5 along an axial direction of the vacuum rod 5. The nozzle member 4 fitted in the vacuum rod 5 is urged downward in the drawing by an urging force of a compression spring 17 stored in parallel to the axial direction in the vacuum rod 5 via a pusher 10. As indicated in FIG. 4, both a contact face 10a of the pusher 10 and a contact face 4b of the fitting part 4a are planar, so that the pusher 10 and fitting part 4a are held in facing contact with each other. The air path 11 is formed in the vacuum rod 5 and fitting part 4a to introduce the air of a negative pressure. A plug 407 is press-fitted at the contact face 4b to shut a hole used when the air path 11 is provided in the fitting part 4a.
The nozzle member 4 urged downward as in the drawing is retained in the vacuum rod 5 by a structure described below. Recess parts 401a, 401b of a suitable length are formed in an axial direction of the nozzle member 4 in an outer circumferential surface of the fitting part 4a. The recessed parts are separated approximately 180.degree. in the circumferential direction of the fitting part 4a. Steel balls 12a, 12b are pressed into the recessed parts 401a, 401b by means of compression springs 13a, 13b exerting an urging force in a direction orthogonal to the axial direction of the nozzle member 4. As shown in FIG. 5, when the steel ball 12a pressed into the recessed part 401a by the compression spring 13a contacts a side wall 403 of the recessed part 401a, a circumferentially rotational force in a counterclockwise direction is applied to the nozzle member 4. Meanwhile, when the steel ball 12b is pressed against a bottom face 402 of the recessed part 401b by the urging force of the compression spring 13b, the circumferential rotation of the nozzle member 4 by the above-described rotational force is restricted. In this construction, the nozzle member 4 is prevented from rotating in the circumferential direction unexpectedly. Moreover, since the steel balls 12a, 12b contact axial end parts 404, 404 of the recessed parts 401a, 401b , the nozzle member 4 is restricted from moving downward in the drawing and is maintained in the vacuum rod 5.
The structure of a mounting head and a nozzle member in a prior example (2) will be discussed with reference to FIG. 6.
A fitting part 14a of a nozzle member 14 is formed cylindrical, with an air path 11 formed thereinside. The fitting part 14a is fitted detachably at a front end part in a vacuum rod 15 along an axial direction of the vacuum rod 15. A torsion coil spring 19 is stored along the axial direction in the vacuum rod 15 so as to urge the nozzle member 14 in a circumferential direction of the nozzle member 14. A cylindrical shank 18 is set along the axial direction in the vacuum rod 15 between the torsion coil spring 19 and nozzle member 14. A rotational force in the circumferential direction by the torsion coil spring 19 is transmitted via the shank 18 to the nozzle member 14. At a part of the nozzle member 14 which contacts the shank 18, the nozzle member 14 projects conically and the shank 18 is recessed like a mortar, as indicated in the drawing. The nozzle member 14 and shank 18 are accordingly kept in facing contact with each other.
A recessed part 40 is formed in an outer circumferential surface of the shank 18 over a predetermined distance along the axial direction. A pin 20 is inserted from an outer face of the vacuum rod 15 into the recessed part 40 and engaged with the recessed part 40, whereby the shank 18 is restricted against rotation in the circumferential direction. A recessed part 405 is also formed over the entire circumference of the fitting part 14a at a part of the outer circumferential face of the fitting part 14a. A steel ball 16 is fitted in a through-hole 406 formed in the vacuum rod 15, which is urged by an elastic body 17 in a direction orthogonal to the axial direction of the nozzle member 14. When the steel ball 16 is meshed with the recessed part 405, the fitting part 14a is controlled to not move in the axial direction of the vacuum rod 15. The structure of the example (2) is disclosed, for example, in Examined Japanese Patent Publication No. 7-24357 and Unexamined Japanese Laid-Open Patent Publication No. 4-133400.
Now, the structure of a mounting head and a nozzle member in a prior example (3) will be discussed with reference to FIG. 7. The structure shown in FIG. 7 is approximately equivalent to the structure of FIG. 6 and therefore only a difference therebetween will be depicted here. The same component members as those of FIG. 6 are designated by the same reference numerals in FIG. 7.
In the structure of FIG. 7, a compression spring 21 is installed in place of the torsion coil spring 19. The nozzle member 14 is urged downward by the compression spring 21.
Structures of the examples (1)-(3) have drawbacks which will be described below.
Specifically, in the mounting head of the example (1) of the structure in FIGS. 4 and 5, the force restricting the rotation of the nozzle member 4 in the circumferential direction depends on the balance of elasticities of the compression springs 13a, 13b, and therefore is unstable. Mounting accuracy for electronic components is disadvantageously reduced. On the other hand, if the urging forces of the compression springs 13a, 13b are increased to enlarge the strength to restrict the rotation of the nozzle member 4, it becomes difficult for the steel balls 12a, 12b to retreat outwardly from the recessed parts 401a, 401b, whereby the nozzle member 4 cannot be attached/detached easily to the mounting head in the simple one-touch operation, or it is diificult for the nozzle member 4 hard to slide in the axial direction.
In the structure of the example (2) in FIG. 6, the torsion coil spring 19 and shank 18 are used to urge the nozzle member 14 in the circumferential direction to thereby restrict the unexpected rotation of the nozzle member 14 in the circumferential direction. However, if the torsional force of the torsion coil spring 19 is weak, the nozzle member 14 readily rotates in the circumferential direction, thereby decreasing the accuracy for mounting of the electronic components. In contrast, if the torsional force of the torsion coil spring 19 is too strong, too much friction force acts between the recess part 40 of the shank 18 and the pin 20 and, and it becomes difficult to slide the nozzle member 14 in the axial direction.
In addition, it is easy for an error to occur during assembly, in that the torsion coil spring 19 may be installed in the vacuum rod 15 without being twisted.
In the structure of the example (3) of FIG. 7, since the nozzle member 14 is not urged in the circumferential direction, the recessed part 40 of the shank 18 is not held in tight contact with the pin 20; in other words, the nozzle member 14 may accidentally rotates in the circumferential direction.